Problem

When attempting to set the resolution of my 4K external display to 3840x2160, the external display loses signal and moments later the entire system hangs.

The display is connected to my XPS 13 9350 Developer Edition running Ubuntu 16.04 using a USB-C to DisplayPort adapter.

Hardware:

• Machine: Dell XPS 13 9350 (3200x1800 resolution display version)
• OS Version: Ubuntu 16.04
• Display: Dell P2415Q
• Adapters:
  • VicTop Type C to DisplayPort Adapter
  • BENFEI USB 3.1 Type C to Displayport Adapter

Attempted Fixes

Setting Resolution Manually

I have tried using xrandr to manually set the mode and refresh rate of the display. Setting it to 4K at 60Hz shows the same problems as setting it in the GUI but if I set it to 4K at 30Hz it works fine.

Doesn't work: xrandr --output DP1 --mode 3840x2160 -r 60.00
Does work : xrandr --output DP1 --mode 3840x2160 -r 29.98

Multiple Adapters

I have attempted using multiple different USB-C to DisplayPort adapters, both of which give the impression that they are capable of 4K resolution at 60Hz. The adapter used does not appear to make a difference to the problem.

Kernel Update

I have updated the kernel to version 4.6 in case better support was added for the integrated Iris graphics. This does not appear to have made any difference.

I hope the steps I have taken that are documented above will help to diagnose the problem.

Solution 1:

Having the same issue with the XPS 9350 (QHD+, BIOS v1.4.4) and external monitor Dell P2415Q. I am using the Plugable USB-C to DisplayPort Adapter Cable.

Upgrading the kernel to v4.8-rc2 seems to solve this problem. I am writing this post on the external monitor running at 3840x2160 60Hz.

Having said that, it is pretty unstable. It crashes often when connecting/disconnecting the adapter and there are some graphical artefacts that appear when moving the mouse and windows around.

My hope is that the final version of the kernel will iron out these issues or at least kernel 4.9 will.

UPDATE: Ubuntu (Gnome) 16.10 works great for the configuration above. No issues so far, except some monitor flickering from time to time.